Individual variation in drug responses

TABLE 13.1-2. Selected Drug Transporters Associated with Individual Variations in Drug Response... 

Ethnic differences have been shown to influence response to psychotropic medications. Much of the focus on the explanation for such differences has been on drug-metabolizing (CYP) enzymes of the liver and their sway over pharmacokinetic factors. It is now well recognized that differences in the distribution of polymorphic variants of CYP enzymes exist between different ethnic groups. However, within ethnic groups there are considerable inter-individual variations in drug kinetics, which may not be accounted for solely by genetic variation. Responses to pharmacotherapy are multifaceted and involve the interaction of environmental and... 

Four general mechanisms may contribute to variation in drug responsiveness among patients or within an individual patient at different times. 

It is commonly agreed that the signal transduction cascade, which is much less understood, is also of tremendous importance in mediating the effect of psychotropics. Components of this cascade include G proteins, ion channels, second messengers, and protein kinases (Manji et al. 1995). Interindividual and crossethnic variations in the genes coding these proteins likely exist and may also be responsible for the individual variability in drug response observed clinically. 

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